No, you can't change the contribution amount in the first box of the "Let's enter [name]'s HSA contributions" screen - it comes from code W in box 12 on the W-2. The number with code W in box 12 on the W-2, also should not be changed, since this reports the amount of HSA contributions that your employer reported going to your HSA custodian.
Typically, a taxpayer in your situation shows excess contribution when they double reported their own contributions, both as payroll deductions (code W in box 12 of the W-2), and also as "personal" contributions made directly to the HSA.
No dollars that rightly belong with the code W amount should be reported anywhere else on the return. Thus, if the code W amount contains contributions made by both the employer and the taxpayer, then this number must not be changed.
The term "employer contribution" confuses most taxpayers. It does not refer to the source of the dollars, but to how the dollars were handled. For example, the code W amount is removed from Wages in boxes 1, 3, and 5 on the W-2. Yes, this means that "employer contributions" are not subject to federal income taxes, Social Security taxes, nor Medicare taxes. This is as opposed to the "personal" HSA contributions that appear on line 13 on part II of Schedule 1 (1040) - these are removed from your taxable income, so not subject to federal income taxes, but they are subject to Social Security and Medicare taxes.
For this reason, it is better for most taxpayers to contribute via their employer through payroll deductions (the code W amount), and not by check or ACH transfer. Indeed, it is common for most taxpayers to contribute most of their annual amount by payroll deduction, and to make a personal contribution at the end of the year when they know how close their contributions are.
So please look at the second paragraph, and see if this is what you did. The second line on the "Let's enter [name]'s HSA contributions" screen should contain ONLY those dollars that you send directly to the HSA, not through your employer.
@strental
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